We compared small mammals in Gulf cordgrass (Spartina spartinae) to coastal-prairie and low-marsh, Spartina alterniflora communities, and we considered the effect of standing-crop biomass and nutrient concentration in plants in the Gulf cordgrass community on dynamics of populations of small mammals. We predicted lower species richness and density of small mammals and shorter residence time in Gulf cordgrass because of little vertical habitat structure, sparse ground cover, and low abundance of dicots, plants that contain nutrients necessary for reproduction by hispid cotton rats (Sigmodon hispidus). Richness in Gulf cordgrass (seven species of rodents) was similar to coastal prairie (six species plus three non-native rodents) with S. hispidus and fulvous harvest mice (Reithrodontomys fulvescens) numerically dominant in both communities. Density of S. hispidus was higher in Gulf cordgrass likely reflecting high standing-crop biomass; however, lack of ground cover contributed to low residence time. Low residency and increase in density during months of increase in density in coastal prairie indicated that Gulf cordgrass functioned as a dispersal sink from adjacent coastal prairie. Density and residency of R. fulvescens were lower in Gulf cordgrass likely reflecting lower quality of habitat because of lack of vertical structure. Low biomass of dicots in Gulf cordgrass would seem to limit availability of nutrients, but nutrients in green stems of S. spartinae were sufficient for growth and reproduction for S. hispidus.